JP7528633B2 - Fixing device, image forming apparatus - Google Patents

Description

The present invention relates to a fixing device and an image forming apparatus.

Fixing devices used in electrophotographic image forming apparatuses widely use a fixing film method that provides a fast heating start-up. One technique is to form a fixing nip by contacting a pressure roller with a nip forming member via a thin fixing film, and to use a lubricant between the inner surface of the fixing film and the surface of the nip forming member. Another technique is to form the nip forming member with a heat transfer auxiliary member that contacts the inner surface of the fixing film and a nip support member that supports the heat transfer auxiliary member (for example, Patent Document 1).

In Patent Document 1, the temperature deviation in the longitudinal direction of the fixing film can be reduced by using metals with high thermal conductivity such as copper and aluminum for the heat transfer assistant member. In other words, it is possible to suppress the temperature rise in non-paper passing areas that occurs when small-sized paper is passed through, and to increase the continuous productivity of small-sized paper. However, there is a problem that the heat transfer assistant member with high thermal conductivity easily takes heat from the fixing film, resulting in a long warm-up time.

The present invention aims to provide a fixing device that can prevent the warm-up time from becoming too long.

The fixing device of the present invention is configured as a fixing device having a rotatable fixing member, a rotatable pressure member arranged opposite the fixing member, a heat source for heating the fixing member, a nip forming member for forming a fixing nip between the pressure member via the fixing member, and a support member for supporting the nip forming member, characterized in that the fixing device further includes a portion where the nip forming member and the support member are in thermal contact in an area other than the area where the nip forming member forms a nip, and further includes a contact/separation means for switching between contact and separation between the nip forming member and the support member .

The present invention makes it possible to prevent the warm-up time from becoming too long.

1 is a schematic diagram illustrating the overall configuration of a printer according to an embodiment of the present invention. FIG. 2 is a diagram illustrating an example of the configuration of the fixing device illustrated in FIG. 1 . 3 is a diagram illustrating an example of the configuration of a main part of the fixing device illustrated in FIG. 2 . FIG. 3 is a perspective view of a main part of the fixing device shown in FIG. 2 . FIG. 3 is a diagram illustrating an example of the configuration of a main part of the fixing device illustrated in FIG. 2 (contact and separation by a cam); 3 is a diagram illustrating an example of the configuration of a main part of the fixing device illustrated in FIG. 2 (contact and separation by a wedge member); 3 is a diagram illustrating an example of the configuration of a main part of the fixing device illustrated in FIG. 2 (connection and separation by a connection member).

The following describes an embodiment of the present invention. The present invention is characterized by the fact that in a fixing device that transfers and fixes a toner image, a part of a heat equalizing plate (burning pad) that comes into contact with a fixing stay (support member) can be attached or detached depending on the situation. The above-mentioned features of the present invention are explained in detail below with reference to the following drawings.

Hereinafter, an embodiment in which the present invention is applied to a laser printer (hereinafter referred to as "printer") 100, which is an electrophotographic image forming device, will be described. FIG. 1 is a schematic diagram of the overall printer according to this embodiment. This printer 100 has a photoconductor drum 21 as a latent image carrier. The photoconductor drum 21 is rotated in the direction of the arrow A in the figure, and its surface is uniformly charged by a charging roller as a uniform charging means that contacts the photoconductor drum 21. After that, the photoconductor drum 21 is scanned and exposed based on image information by an optical writing unit 9 as a latent image forming means, and an electrostatic latent image is formed on the surface of the photoconductor drum 21. Note that the uniform charging means and the latent image forming means may be different from the charging roller and the optical writing unit 9. The electrostatic latent image formed on the photoconductor drum 21 is developed by a developing device 10, which will be described later, and a toner image is formed on the photoconductor drum 21. The toner image formed on the photosensitive drum 21 is transferred by a transfer unit as a transfer means having a transfer roller 11 onto a transfer paper as a transfer material transported from a paper feed cassette 8 via a paper feed roller 7 and a pair of registration rollers 6. After the transfer is completed, the toner image on the transfer paper is fixed by a fixing device 4 as a fixing means, and the transfer paper is discharged outside the machine. Residual toner that has not been transferred and remains on the photosensitive drum 21 is removed from the surface of the photosensitive drum 21 by a cleaning unit 12 as a cleaning means. Residual charge on the photosensitive drum 21 is also removed by a discharge lamp as a discharge means.

2 is a diagram showing an example of the configuration of the fixing device shown in FIG. 1. FIG. 2 shows the fixing device 4, which is heated by a pressure roller 22 and a fixing belt (fixing sleeve) 21, which are pressure rotating bodies, and a halogen heater 23, which is a heat source, in the fixing device 4. A nip forming member 24 held by a fixing stay 25 is provided in the fixing belt 21, and slides directly (or indirectly via a sliding sheet not shown) with the inner surface of the fixing belt 21. As will be described later, the nip forming member 24 is formed by a scorching pad 241, which is a heat transfer auxiliary member that contacts the inner surface of the fixing belt 21, and a nip support member 242 that supports the scorching pad 241. As will be described later, the nip forming member 24 has a portion where the scorching pad 241 and the fixing stay 25 that constitute the nip forming member 24 can be thermally contacted (or thermally bonded) in an area other than the area that forms the nip portion N. In FIG. 2, the shape of the nip portion N is concave, but it may be flat or have other shapes. When the nip N is concave, the leading edge of the paper is discharged toward the pressure roller 22, improving separation and reducing the occurrence of jams.

The pressure roller 22 has a silicone rubber layer on a metal roller, and a release layer (PFA or PTFE layer) is provided on the surface to provide releasability. The pressure roller 22 rotates by a driving force transmitted via gears from a driving source such as a motor provided in the printer 100, which is an image forming apparatus. The pressure roller 22 is pressed against the fixing belt 21 by a spring or the like, and has a predetermined nip width as the rubber layer is crushed and deformed. The pressure roller 22 may be a solid roller, but a hollow roller has less heat capacity.

The pressure roller 22 may also have a heating source such as a halogen heater. The silicone rubber layer may be solid rubber, but if there is no heater inside the pressure roller 22, sponge rubber may be used. Sponge rubber is more preferable because it has higher insulation properties and is less likely to take away heat from the fixing belt. The belt is a metal belt such as nickel or SUS, or an endless belt (or film) made of a resin material such as polyimide. The surface layer of the belt has a release layer such as a PFA or PTFE layer, which provides release properties so that toner does not adhere to it. An elastic layer formed of a silicone rubber layer or the like may be present between the base material of the belt and the PFA or PTFE layer. If there is no silicone rubber layer, the heat capacity is reduced and the fixing property is improved, but when the unfixed image is crushed and fixed, the subtle unevenness of the belt surface is transferred to the image, leaving a citrus peel-like mark on the solid part of the image.

To improve this, the silicone rubber layer must be at least 100 μm thick. By deforming the silicone rubber layer, subtle irregularities are absorbed, improving the citrus skin image. The hollow pipe-shaped metal body is made of aluminum, iron, stainless steel, or other metals. The metal body shown in the figure is circular, but it may be rectangular or have other cross-sectional shapes. In this case, if the support is heated by radiant heat from a halogen heater or the like, the support surface can be insulated or mirror-finished to prevent heating, reducing unnecessary energy consumption.

The heat source for heating the metal hollow thermal conductor may be the halogen heater shown in the figure, an IH (Induction Heating) coil, a resistance heating element, a carbon heater, etc. The belt rotates together with an external roller. In the case of FIG. 2, the pressure roller 22 is rotated by a drive source (not shown), and the belt rotates when the drive force is transmitted to the belt at the nip portion N. With the above configuration, it is possible to realize a fixing device that is inexpensive and has a quick warm-up time.

In this embodiment, inside the fixing belt 21, there are arranged a nip forming member 24 that forms a nip portion N with the pressure roller 22, the fixing stay 25 that supports the load on the nip forming member 24, a halogen heater 23 as a heat source, and a flange that holds them. Furthermore, the fixing device 4 has a shielding member 27 between the halogen heater 23 in the fixing belt 21 and the fixing belt 21 that blocks the heat of the halogen heater 23. This shielding member 27 needs to have very high heat resistance, so it is desirable to make it from aluminum, iron, stainless steel, etc.

The heater 23 has a central heater 23A and an end heater 23B, each of which directly heats the fixing belt 201 from the inner periphery side by radiant heat. As described below, each of the heaters has a different heat generating area in the direction of the rotation axis of the fixing belt 21, and heats a different area of the fixing belt 21. As an example of the heater 23, a halogen heater is used, but this is not limited thereto, and it may be a ceramic heater that heats the fixing member by contacting it, or an IH heater that heats the fixing member from inside using electromagnetic induction.

Next, the nip forming member 24 may be an assembly consisting of multiple resin and metal parts, or may be made of a single resin or metal. The heat equalizing member surface arranged on the nip surface is arranged to equalize the temperature in the axial direction. In the past, in a fixing device using a sliding nip, in order to reduce the sliding resistance of the nip part N, a sliding sheet made of fibers such as PTFE is impregnated with a lubricant such as silicone oil and fixed to the resin nip forming member. The first role of the resin pad in this configuration is to hold the sliding sheet. The sheet is arranged in a manner that it is wrapped around the resin pad and fixed with screws on the back side of the resin pad. In this embodiment, in order to enhance the heat equalizing effect more than the sliding sheet, a metal plate made of aluminum or copper (or a combination of these materials) with a sliding coating formed on the surface (heat equalizing pad) is proposed as the nip forming member 24. In this embodiment, the scorching pad 241, which is a heat transfer auxiliary member supported by the nip support member 242 constituting the nip forming member 24, is covered with the coating. In this way, the sliding film adheres closely to the surface of the scorching pad 241, so high thermal conductivity can be maintained, which is expected to reduce the rise in temperature at the end of the fixing device when continuous paper is passed through. On the other hand, there is an issue that the high thermal conductivity at the start-up causes heat from the surface of the fixing member to flow into the inside, lengthening the recovery time (warm-up time).

In order to solve this problem, this embodiment proposes a configuration having a cam 51 as a means for moving the scorching pad 241 closer and farther as shown in Figures 3 and 4. A conventionally known mechanism (e.g., a flat cam with a rotating plate) can be used for the configuration of the cam 51. Figure 3 is a diagram showing an example of the configuration of the main part of the fixing device shown in Figure 2. Figure 4 is a perspective view of the main part of the fixing device shown in Figure 2. As shown in these figures, the heat-equalizing pad 241 constituting the nip forming member 24 has a contact area P that is in thermal contact with the fixing stay 25, and heat can be released from this area to the fixing stay 25. The contact area P of the scorching pad 241 is in thermal contact (or thermally coupled) with the fixing stay 25 in an area other than the area where the nip forming member 24 forms the nip portion N.

In addition, the fixing device 4 is provided with a central heater 23A that mainly heats the central portion of the fixing belt 21 in the longitudinal direction, and an end heater 23B that mainly heats the end portions of the fixing belt 21 in the longitudinal direction, as heat sources for heating the fixing belt 21. The contact portion P is provided at approximately the same position as the heating width of the central heater 23A. In FIG. 4, it is provided near both ends of the central heater 23A in the longitudinal direction. In other words, the contact portion P is provided outside the heating width of the central heater 23A in the longitudinal direction and inside the heating width of the end heater 23B in the longitudinal direction. Since the thermal capacity of the fixing stay 25 is sufficiently larger than that of the heat equalizing pad 241, it is expected to reduce the temperature rise at the end portions of the fixing device. On the other hand, when the device is started up, the contact portion is kept in a non-contact state by the cam 51, which is a contact/separation means, and heat can be prevented from flowing out from the heat equalizing pad 241, allowing for high-speed recovery.

In FIG. 4, the contact portion P of the scorching pad 241 moves in the ZC direction due to the rotation of the cam 51, which is the contact/separation means. More specifically, in FIG. 5, the cam 51 rotates in the counterclockwise direction D, causing the contact portion P of the scorching pad 241 to contact the upper surface of the fixing stay 25. Conversely, the cam 51 rotates in the opposite direction to the direction D, causing the contact portion P of the scorching pad 241 to move away from the upper surface of the fixing stay 25. Note that, although FIG. 4 illustrates a configuration in which the cams 51 are disposed at two locations at the ends in the YC direction, which is the longitudinal direction, the positions can be determined arbitrarily. The cams 51 are controlled, for example, by a control unit (not shown) provided in the fixing device 4 or the printer 100. Such control is performed when the device is started up and when continuous paper is passed through, that is, the contact/separation state between the scorching pad 241 constituting the nip forming member 24 and the fixing stay 25 can be changed according to the temperature of the fixing belt 21, thereby solving the problem of the long warm-up time caused by the high thermal conductivity heat transfer auxiliary member easily taking heat from the fixing film. Specifically, when the device is started up, the cam 51, which is the contact/separation means, lifts the contact part P of the scorching pad 241 constituting the nip forming member from the fixing stay 25, separating the heat equalizing pad 241 from the fixing stay 25. On the other hand, for continuous paper passing, the cam 51 is released to switch the heat equalizing pad 241 and the fixing stay 25 to a contact state, thereby preventing the warm-up time from being long.

The contact means may take the form of the cam 51 shown in FIG. 3-5, or may take the form of inserting a wedge-shaped member made of a heat insulating material, as shown in FIG. 6. In FIG. 6, the wedge-shaped contact member 61 is provided on the upper surface of the fixing stay 25, and the tip of the contact member 61 is inserted between the lower surface of the heat pad 241 and the upper surface of the fixing stay 25, so that the contact portion P of the heat pad 241 forming the nip forming member is lifted from the fixing stay 25, and the heat equalizing pad 241 and the fixing stay 25 are separated. Conversely, the inserted contact member 61 can be removed to bring them into contact.

As another example, as shown in FIG. 7, a clearance may be provided between the contact portion P of the heat equalizing pad 241 and the fixing stay 25, and when the end temperature of the fixing device rises due to continuous paper passing, the clearance may be filled with a material having good thermal conductivity, and the heat equalizing pad 241 and the fixing stay 25 may be thermally contacted. FIG. 7 shows the state in which the connecting member 71 having good thermal conductivity is inserted and inserted into the clearance formed at the contact portion P between the heat equalizing pad 241 and the fixing stay 25. The figure shows the state before the connecting member 71 is inserted into the clearance, and the connecting member 71 is inserted and inserted into the contact portion P (inserted to the left in the figure), so that the heat equalizing pad 241 and the fixing stay 25 are thermally contacted through the connecting member 71. Unlike the case shown in FIG. 6, the connecting member 71 is preferably made of a material having good thermal conductivity.

In the past, when increasing the volume of a heat transfer auxiliary member to improve its end temperature rise mitigation performance, there was a problem that the heat capacity also increased, which reduced energy-saving performance such as warm-up time. However, as described above, according to this embodiment, the heat equalizing pad constituting the nip forming member is provided with a portion that contacts the fixing stay, and this portion can be brought into contact with and separated from the fixing stay depending on the situation. With this configuration, for example, at start-up, the heat equalizing pad and the fixing stay can be separated to prevent heat from flowing out, and therefore the recovery time can be prevented from worsening. On the other hand, when the heat equalizing pad and the fixing stay are in contact with each other, the heat accumulated at the end of the fixing sleeve during continuous paper feed can be released to the fixing stay through the heat equalizing plate, so that the end temperature rise can be suppressed while suppressing the heat capacity of the heat equalizing plate.

Reference Signs List 100 Laser printer 4 Fixing device 21 Fixing belt 22 Pressure roller 23 Halogen heater 23A Center heater 23B End heater 24 Nip forming member 241 Burning pad 242 Nip support member 25 Fixing stay 51 Cam 61 Wedge member 71 Connection member

JP 2018-169467 A

Claims (5)

A fixing device including a rotatable fixing member, a rotatable pressure member disposed opposite to the fixing member, a heat source for heating the fixing member, a nip forming member for forming a fixing nip between the fixing member and the pressure member, and a support member for supporting the nip forming member,
the nip forming member has a portion where the nip forming member and the support member can be in thermal contact with each other in a region other than a region where the nip forming member forms a nip ;
The fixing device further comprises a contact/separation unit that switches between contact and separation between the nip forming member and the support member . 2. The fixing device according to claim 1,
13. A fixing device, comprising: a fixing member that is fixed to the nip forming member; a fixing member that is fixed to the support member; A fixing device including a rotatable fixing member, a rotatable pressure member disposed opposite to the fixing member, a heat source for heating the fixing member, a nip forming member for forming a fixing nip between the fixing member and the pressure member, and a support member for supporting the nip forming member,
the nip forming member has a portion where the nip forming member and the support member can be in thermal contact with each other in a region other than a region where the nip forming member forms a nip;
the heat source for heating the fixing member includes a center heater for mainly heating a central portion of the fixing member in a longitudinal direction, and end heaters for mainly heating end portions of the fixing member in the longitudinal direction;
The fixing device according to claim 1, wherein the contactable portion is provided at a position substantially equal to a heating width of the central heater. 2. The fixing device according to claim 1,
the heat source for heating the fixing member includes a center heater for mainly heating a central portion of the fixing member in a longitudinal direction, and end heaters for mainly heating end portions of the fixing member in the longitudinal direction;
a contactable portion of the fixing device that is located outside a heating width region of the central heater and inside a heating width region of the end heater; An image forming apparatus comprising the fixing device according to any one of claims 1 to 4.

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